Cysteine String Protein Controls Two Routes of Export for Misfolded Huntingtin

Extracellular vesicles (EVs) are secreted vesicles of diverse size and cargo that are implicated in the cell-to-cell transmission of disease-causing-proteins in several neurodegenerative diseases. Mutant huntingtin, the disease-causing entity in Huntington’s disease, has an expanded polyglutamine track at the N terminus that causes the protein to misfold and form toxic intracellular aggregates. In Huntington’s disease, mutant huntingtin aggregates are transferred between cells by several routes. We have previously identified a cellular pathway that is responsible for the export of mutant huntingtin via extracellular vesicles. Identifying the EV sub-populations that carry misfolded huntingtin cargo is critical to understanding disease progression. In this work we expressed a form of polyglutamine expanded huntingtin (GFP-tagged 72Qhuntingtinexon1) in cells to assess the EVs involved in cellular export. We demonstrate that the molecular chaperone, cysteine string protein (CSPα; DnaJC5), facilitates export of disease-causing-polyglutamine-expanded huntingtin cargo in 180–240 nm vesicles as well as larger 10–30 μm vesicles.

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The Ubiquitin-Proteasome System in Huntington’s Disease: Are Proteasomes Impaired, Initiators of Disease, or Coming to the Rescue?

Biochemistry Research International ◽

10.1155/2012/837015 ◽

2012 ◽

Vol 2012 ◽

pp. 1-12 ◽

Cited By ~ 35

Author(s):

Sabine Schipper-Krom ◽

Katrin Juenemann ◽

Eric A. J. Reits

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Protein A ◽

Ubiquitin Proteasome System ◽

Mutant Huntingtin ◽

Polyglutamine Expansion ◽

Ubiquitin Proteasome ◽

Intracellular Aggregates ◽

Polyglutamine Aggregation

Huntington’s disease is a progressive neurodegenerative disease, caused by a polyglutamine expansion in the huntingtin protein. A prominent hallmark of the disease is the presence of intracellular aggregates initiated by N-terminal huntingtin fragments containing the polyglutamine repeat, which recruit components of the ubiquitin-proteasome system. While it is commonly thought that proteasomes are irreversibly sequestered into these aggregates leading to impairment of the ubiquitin-proteasome system, the data on proteasomal impairment in Huntington’s disease is contradictory. In addition, it has been suggested that proteasomes are unable to actually cleave polyglutamine sequencesin vitro, thereby releasing aggregation-prone polyglutamine peptides in cells. Here, we discuss how the proteasome is involved in the various stages of polyglutamine aggregation in Huntington’s disease, and how alterations in activity may improve clearance of mutant huntingtin fragments.

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Indirect inhibition of 26S proteasome activity in a cellular model of Huntington’s disease

The Journal of Cell Biology ◽

10.1083/jcb.201110093 ◽

2012 ◽

Vol 196 (5) ◽

pp. 573-587 ◽

Cited By ~ 116

Author(s):

Mark S. Hipp ◽

Chetan N. Patel ◽

Kirill Bersuker ◽

Brigit E. Riley ◽

Stephen E. Kaiser ◽

...

Keyword(s):

Neurodegenerative Diseases ◽

Huntington's Disease ◽

Huntington’S Disease ◽

Proteasome Activity ◽

26S Proteasome ◽

Mutant Huntingtin ◽

Cellular Model ◽

Cytoplasmic Inclusions ◽

Impaired Function ◽

Terminal Fragment

Pathognomonic accumulation of ubiquitin (Ub) conjugates in human neurodegenerative diseases, such as Huntington’s disease, suggests that highly aggregated proteins interfere with 26S proteasome activity. In this paper, we examine possible mechanisms by which an N-terminal fragment of mutant huntingtin (htt; N-htt) inhibits 26S function. We show that ubiquitinated N-htt—whether aggregated or not—did not choke or clog the proteasome. Both Ub-dependent and Ub-independent proteasome reporters accumulated when the concentration of mutant N-htt exceeded a solubility threshold, indicating that stabilization of 26S substrates is not linked to impaired Ub conjugation. Above this solubility threshold, mutant N-htt was rapidly recruited to cytoplasmic inclusions that were initially devoid of Ub. Although synthetically polyubiquitinated N-htt competed with other Ub conjugates for access to the proteasome, the vast majority of mutant N-htt in cells was not Ub conjugated. Our data confirm that proteasomes are not directly impaired by aggregated N-terminal fragments of htt; instead, our data suggest that Ub accumulation is linked to impaired function of the cellular proteostasis network.

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Faculty Opinions recommendation of TR-FRET-based duplex immunoassay reveals an inverse correlation of soluble and aggregated mutant huntingtin in huntington's disease.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717951315.793456621 ◽

2012 ◽

Author(s):

Roger Barker ◽

Wei-Li Kuan

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Inverse Correlation ◽

Mutant Huntingtin

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Faculty Opinions recommendation of Mutant huntingtin fragmentation in immune cells tracks Huntington's disease progression.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717960625.793464988 ◽

2012 ◽

Author(s):

Stefano Di Donato

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Disease Progression ◽

Immune Cells ◽

Mutant Huntingtin

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Identification of Full-Length Wild-Type and Mutant Huntingtin Interacting Proteins by Crosslinking Immunoprecipitation in Mice Brain Cortex

Journal of Huntington s Disease ◽

10.3233/jhd-210476 ◽

2021 ◽

pp. 1-13

Author(s):

Karen A. Sap ◽

Arzu Tugce Guler ◽

Aleksandra Bury ◽

Dick Dekkers ◽

Jeroen A.A. Demmers ◽

...

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Brain Cortex ◽

Full Length ◽

Biological Processes ◽

Interacting Proteins ◽

Mutant Huntingtin ◽

Wild Type ◽

Mutant Huntingtin Protein ◽

Mice Brain

Background: Huntington’s disease is a neurodegenerative disorder caused by a CAG expansion in the huntingtin gene, resulting in a polyglutamine expansion in the ubiquitously expressed mutant huntingtin protein. Objective: Here we set out to identify proteins interacting with the full-length wild-type and mutant huntingtin protein in the mice cortex brain region to understand affected biological processes in Huntington’s disease pathology. Methods: Full-length huntingtin with 20 and 140 polyQ repeats were formaldehyde-crosslinked and isolated via their N-terminal Flag-tag from 2-month-old mice brain cortex. Interacting proteins were identified and quantified by label-free liquid chromatography-mass spectrometry (LC-MS/MS). Results: We identified 30 interactors specific for wild-type huntingtin, 14 interactors specific for mutant huntingtin and 14 shared interactors that interacted with both wild-type and mutant huntingtin, including known interactors such as F8a1/Hap40. Syt1, Ykt6, and Snap47, involved in vesicle transport and exocytosis, were among the proteins that interacted specifically with wild-type huntingtin. Various other proteins involved in energy metabolism and mitochondria were also found to associate predominantly with wild-type huntingtin, whereas mutant huntingtin interacted with proteins involved in translation including Mapk3, Eif3h and Eef1a2. Conclusion: Here we identified both shared and specific interactors of wild-type and mutant huntingtin, which are involved in different biological processes including exocytosis, vesicle transport, translation and metabolism. These findings contribute to the understanding of the roles that wild-type and mutant huntingtin play in a variety of cellular processes both in healthy conditions and Huntington’s disease pathology.

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